Shift Register Unit and Driving Method Thereof, Gate Driving Device and Display Device

ABSTRACT

The present disclosure provides a shift register unit and a driving method thereof, a gate driving device and a display device. The shift register unit includes an input circuit, an output circuit, a pull-down circuit, a first pull-down control circuit, and a second pull-down control circuit, wherein the second pull-down control circuit is provided with a first pull-down compensation transistor and a second pull-down compensation transistor and connected to a second power supply voltage, to compensate a threshold voltage drift of a second pull-down control transistor in the second pull-down control circuit so as to avoid abnormality of the shift register unit which would be caused by the threshold voltage drift of the second pull-down control transistor driven by a long-time high voltage, thereby ensuring the stability of the shift register unit.

This application claims priority to and the benefit of Chinese Patent Application No. 201710890439.X filed on Sep. 27, 2017, which application is incorporated herein in its entirety.

TECHNICAL FIELD

The present disclosure relates to a shift register unit and a driving method thereof, a gate driving device and a display device.

BACKGROUND

A thin film transistor liquid crystal display (TFT-LCD) is widely applied in a variety of fields of production and life, and it adopts a progressive scanning matrix display arranged by M*N points. When displaying, the TFT-LCD drives various pixels in the display panel to be displayed through a driving circuit. The driving circuit of the TFT-LCD mainly comprises a gate driving circuit and a data driving circuit. Herein, the data driving circuit is used to sequentially latch the input data at regular time according to a clock signal and input the latched data to data lines of a display panel. A gate driving circuit is generally implemented by a shift register unit. The shift register unit converts the clock signal into a turn-on/turn-off voltage which is output to respective gate lines of the display panel respectively. One gate line on the display panel is always oppositely connected to one shift register unit (i.e., one stage of the shift register unit). Progressive scanning of pixels in the display panel is realized by making the respective shift register units sequentially output the turn-on voltage by turns.

On the other hand, as panel display develops, high resolution and narrow frame become the trend of development. In response to this trend, technique of Gate Driver on Array (GOA) emerges. The GOA technique integrates and manufactures the gate driving circuit of the TFT-LCD on an array substrate directly, thereby replacing a driving chip which is bonded with the outside edge of the panel and is made of silicon chip. Since this technique can make the driving circuit on the array substrate directly, there is no need to bond IC and arrange wirings around the panel, which reduces the manufacturing procedure of the panel, decreases the cost of production, and at the same time improves the integration of the TFT-LCD panel, so that the panel realizes narrow frame and high resolution.

Positive drift would occur to threshold voltages of TFT switches in the GOA driving circuit if the TFT switches are driven by high voltages for a long time, which causes reduction of output voltages of the TFT switches, and further causes abnormity of output signals of the GOA driving circuit, thereby affecting stability of the liquid crystal display panel.

SUMMARY

There are provided in the present disclosure a shift register unit and a driving method thereof, a gate driving device and a display device, which could improve the leakage problem caused by drift of threshold voltages of TFT switches in a GOA driving circuit and enhance stability of the GOA driving circuit.

According to one aspect of the present disclosure, there is disclosed a shift register unit, comprising: an input circuit, whose first terminal receives an input signal of the shift register unit, second terminal is connected to a pull-up node, configured to output the input signal to the pull-up node; an output circuit, whose first terminal is connected to a first clock signal terminal, second terminal is connected to the pull-up node, and third terminal is connected to an output terminal of the shift register unit, configured to output to a first clock signal of the first clock signal terminal to the output terminal under control of the pull-up node; a pull-down circuit, whose first terminal is connected to a pull-down node, second terminal is connected to the pull-up node, third terminal is connected to the output terminal, and fourth terminal is connected to a first power supply voltage terminal, configured to pull down the pull-up node and the output terminal to a first power supply voltage of the first power supply voltage terminal under control of the pull-down node; a first pull-down control circuit, whose first terminal is connected to a second clock signal terminal, second terminal is connected to a first pull-down control node, third terminal is connected to the pull-down node, fourth terminal is connected to the pull-up node, and fifth terminal is connected to the first power supply voltage terminal, configured to: pull down the pull-down node to the first power supply voltage of the first power supply voltage terminal under control of the pull-up node, and output a second clock signal of the second clock signal terminal to the pull-down node under control of the first pull-down control node; and a second pull-down control circuit, whose first terminal is connected to the second clock signal terminal, second terminal is connected to the first power supply voltage terminal, third terminal is connected to the pull-up node, fourth terminal is connected to the first pull-down control node, and fifth terminal is connected to a second power supply voltage terminal, and the second pull-down control circuit being configured to: pull down the first pull-down control node to the first power supply voltage of the first power supply voltage terminal when the pull-up node is at a valid pull-up level, and compensate for the first pull-down control node through a second power supply voltage when the pull-up node is at an invalid pull-up level and the second clock signal is at a first level, so that the first pull-down control node drives the first pull-down control circuit to output the second clock signal to the pull-down node.

According to another aspect of the present disclosure, there is disclosed a driving method of the shift register unit described above, comprising:

receiving an input signal of the shift register unit, and outputting the input signal to a pull-up node, by an input circuit, when the input signal is at a valid input level;

pulling down, by a first pull-down control circuit, a pull-down node to a first power supply voltage of a first power supply voltage terminal, pulling down, by a second pull-down control circuit, a first pull-down control node to the first power supply voltage of the first power supply voltage terminal, and outputting, by an output circuit, a first clock signal of a first clock signal terminal to an output terminal, when the pull-up node is at a valid pull-up level;

compensating for the first pull-down control node through the second power supply voltage when the pull-up node is at an invalid pull-up level and a second clock signal is at a first level, such that the first pull-down control node is maintained at a first voltage, to drive the first pull-down control circuit to output the second clock signal of a second clock signal terminal to the pull-down node;

pulling down, by a pull-down circuit, the pull-up node and the output terminal to the first power supply voltage of the first power supply voltage terminal when the pull-down node is at the valid pull-down level.

According to another aspect of the present disclosure, there is disclosed a gate driving device, comprising a plurality of shift register units connected in series, each of which is the shift register unit described above, wherein except a last shift register unit, an output terminal of each of remaining shift register units is connected to an input terminal of a next adjacent shift register unit; a frame start signal is inputted to an input terminal of a first shift register unit.

According to another aspect of the present disclosure, there is disclosed a display device comprising the gate driving device described above.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferable embodiments of the present disclosure are described in detail by combining with accompanying figures. The above and other purposes, characteristic and advantages of the present disclosure would become clearer, wherein same reference marks are designated to units having a same structure, wherein:

FIG. 1 shows a circuit diagram of a shift register unit;

FIG. 2 shows an operation timing diagram of the shift register unit of FIG. 1;

FIG. 3 shows a block diagram of a shift register unit according to an embodiment of the present disclosure;

FIG. 4 shows an exemplary circuit structure diagram of a shift register unit according to an embodiment of the present disclosure;

FIG. 5 shows an operation timing diagram of the exemplary circuit of the shift register unit in FIG. 4;

FIG. 6 shows an exemplary driving method of a shift register unit according to an embodiment of the present disclosure; and

FIG. 7 shows a schematic diagram of a gate driving device formed by a plurality of shift register units connected in series according to an embodiment of the present disclosure.

DETAILED DESCRIPTION

Technical solutions in embodiments of the present disclosure will be described clearly and completely below by combining with the figures in the embodiments of the present disclosure. Obviously, the embodiments described below are just a part of embodiments of the present disclosure, but not all the embodiments. Based on the embodiments in the present disclosure, all the other embodiments obtained by those ordinary skilled in the art without paying any inventive labor belong to the scope sought for protection in the present disclosure.

Transistors adopted in all the embodiments of the present disclosure can be thin film transistors or field effect transistors or other devices having the same characteristics. In the embodiment, connection manner of a drain and a source of each transistor can be exchanged with each other. Therefore, drains and sources of respective transistors in the embodiments of the present disclosure have no distinction actually. Herein, for the purpose of convenient description, one of a drain and a source of a transistor is called as a first electrode of the transistor, and the other thereof is called as a second electrode of the transistor.

FIG. 1 shows a circuit diagram of a shift register unit. As shown in FIG. 1, the shift register unit 100 comprises first to tenth transistors M1-M10 and a first capacitor C1. Herein, the first transistor M1 functions as an input circuit 11, the third and fourth transistors M3-M4 function as a reset circuit 14, the fifth to eighth transistors M5-M8 function as a pull-down control circuit 15, the ninth and tenth transistor M9-M10 function as a pull-down circuit 13, and the second transistor M2 and the first capacitor C1 function as an output circuit 12.

A first terminal of the input terminal 11 is connected to an input terminal INPUT of the shift register unit and is used to receive an input signal from the input terminal INPUT, a second terminal thereof is connected to a pull-up node PU, and the input circuit 11 is configured to output the input signal received from the input terminal INPUT to the pull-up node PU when the received input signal is at a valid input level.

A first terminal of the output circuit 12 is connected to a first clock signal terminal CLK, a second terminal thereof is connected to the pull-up node PU, a third terminal thereof is connected to an output terminal OUTPUT of the shift register unit, and the output circuit 12 is configured to output a first clock signal of the first clock signal terminal CLK to the output terminal OUTPUT when a pull-up signal of the pull-up node PU is at a valid pull-up level.

A first terminal of the pull-down circuit 13 is connected to a pull-down node PD, a second terminal thereof is connected to the pull-up node PU, a third terminal thereof is connected to the output terminal OUTPUT, and a fourth terminal thereof is connected to a first power supply voltage terminal VSS, and the pull-down circuit 13 is configured to pull down the output terminal OUTPUT and the pull-up node PU to a first power supply voltage of the first power supply voltage terminal VSS when a pull-down signal of the pull-down node PD is at a valid pull-down level.

A first terminal of the reset circuit 14 is connected to a reset signal terminal RESET, a second terminal thereof is connected to the pull-up node PU, a third terminal thereof is connected to the first power supply voltage terminal VSS, and a fourth terminal thereof is connected to the output terminal OUTPUT, and the reset circuit 14 is configured to pull down the pull-up signal of the pull-up node PU and the output signal of the output terminal OUTPUT to the first power supply voltage of the first power supply voltage terminal VSS when a reset signal of the reset signal terminal RESET is at a valid reset level.

A first terminal of the pull-down control circuit 15 is connected to a second clock signal terminal CLKB, a second terminal thereof is connected to the pull-up node PU, a third terminal thereof is connected to the pull-down node PD, a fourth terminal thereof is connected to the first power supply voltage terminal VSS, and the pull-down control circuit 15 is configured to control whether the pull-down circuit 13 performs any operation. For example, the pull-down control circuit 15 generates at the pull-down node PD a pull-down signal being at an invalid pull-down level when the pull-up signal of the pull-up node PU is at the valid pull-up level, and generates at the pull-down node PD a pull-down signal being at a valid pull-down level when the pull-up signal of the pull-up node PU is at an invalid pull-up level and the second clock signal of the second clock signal terminal CLKB is at a first level.

Herein, phase of the first clock signal of the first clock signal terminal CLK is inverted compared to that of the second clock signal of the second clock signal terminal CLKB.

Herein, the first power supply voltage terminal VSS is a low power supply voltage terminal.

Descriptions are given below by taking the transistors being N type transistors as an example. Therefore, the valid input level, the valid pull-up level, the valid reset level, the valid pull-down level, and the first level are high levels.

FIG. 2 shows a timing diagram for various signals when the shift register unit shown in FIG. 1 performs scanning.

In a first phase P1, when the input signal of the input terminal INPUT is at a high level, the first transistor M1 is turned on, and a potential at the pull-up node PU rises to a high level. Since the pull-up node PU is at the high level, both the eighth transistor M8 and the sixth transistor M6 are turned on, so as to pull down respectively the pull-down control node PD_CN and the pull-down node PD to a low level.

In a second phase P2, when the input signal becomes a low level, the first transistor M1 is turned off. At this time, the potential at the pull-up node PU has become the high level, so that the second transistor M2 is turned on, and the output terminal OUTPUT would output a high level. Due to existence of the first capacitor C1, as a potential of the output terminal OUTPUT rises, the potential at the pull-up node PU would further rise. Since the pull-up node PU is still at a high level, both the eighth transistor M8 and the sixth transistor M6 are turned on, so that the pull-down control node PD_CN and the pull-down node PD are maintained at a low level.

In a third phase P3, when a high level is output from the reset signal terminal RESET, the first transistor M1 is turned off, the third transistor M3 and the fourth transistor M4 are turned on, the potential at the pull-up node PU is pulled down to a low level, the second transistor M2, the sixth transistor M6 and the eighth transistor M8 are all turned off. At this time, the second clock signal terminal CLKB outputs a high level, the seventh transistor is turned on, and the pull-down control node PD_CN becomes a high level, so that the fifth transistor M5 is also turned on under a control of the pull-down control node PD_CN, and the pull-down node PD also becomes a high level. In addition, the ninth transistor and the tenth transistor further respectively pull down the pull-up node PU and the output terminal OUTPUT to a low level under a control of the pull-down node PD.

A first electrode and a gate of the seventh transistor M7 in FIG. 1 are always connected to the second clock signal terminal CLKB, and the second clock signal terminal CLKB continuously outputs a pulse signal consisting of alternating high and low levels (as shown in FIG. 2). Under impact of long-time high level voltage, positive drift would occur to the threshold voltage of the seventh transistor M7, which causes an output voltage from a second electrode of the seventh transistor M7 reduced. Since the second electrode of the seventh transistor M7 is connected to the pull-down control node PD_CN, positive drift of the threshold voltage of the seventh transistor M7 would cause that a voltage of the pull-down control node PD_CN during the third phase P3 decreases, which is possible to further cause that the fifth transistor M5 cannot be turned on during the third phase P3, such that the pull-down control circuit cannot work normally. Since the pull-down control circuit is used to control whether the pull-down circuit performs any operation, the pull-down circuit cannot work normally either. For example, the pull-up node PU cannot be pulled down to make it discharge normally, resulting in an abnormal output signal of the shift register unit, thereby affecting the stability of the shift register unit.

In order to solve the above problem, there is provided in the present disclosure a shift register unit, which compensates for the influence of the positive drift of the threshold voltage of the seventh transistor M7 on the voltage of the pull-down control node by adding a related pull-down compensation module in the pull-down control circuit, such that the pull-down control node is capable of driving the pull-down circuit normally, thereby avoiding abnormality of the output signal of the shift register unit, so as to ensure the stability of the shift register unit, prolong the service life of a TFT-LCD on which the shift register unit is applied, and enhance the picture quality of a TFT-LCD display device.

In particular, according to an embodiment of the present disclosure, the positive drift of the threshold voltage of the seventh transistor M7 as shown in FIG. 1 is suppressed by additionally setting a first pull-down compensation transistor and a second pull-down compensation transistor and introducing a second power supply voltage inside the pull-down control circuit of the shift register unit as shown in FIG. 1, so that the pull-down control circuit in the shift register unit can drive the pull-down circuit normally, so as to realize discharging the pull-up node PU and the output terminal OUTPUT reliably.

FIG. 3 shows a block diagram of a shift register unit according to an embodiment of the present disclosure. As shown in FIG. 3, in an embodiment, the shift register unit 300 comprises an input circuit 31, an output circuit 32, a pull-down circuit 33, a first pull-down control circuit 35 and a second pull-down control circuit 36.

A first terminal of the input circuit 31 receives an input signal from an input terminal INPUT of the shift register unit, a second terminal thereof is connected to a pull-up node PU. The input circuit 31 is configured to output the received input signal to the pull-up node PU when the input signal of the input terminal INPUT is at a valid input level.

A first terminal of the output terminal 32 is connected to a first clock signal terminal CLK, a second terminal thereof is connected to the pull-up node PU, a third terminal thereof is connected to the output terminal OUTPUT of the shift register unit. The output circuit 32 is configured to output a first clock signal of the first clock signal terminal CLK to the output terminal OUTPUT when a pull-up signal of the pull-up node PU is at a valid pull-up level.

A first terminal of the pull-down circuit 33 is connected to a pull-down node PD, a second terminal thereof is connected to the pull-up node PU, a third terminal thereof is connected to the output terminal OUTUT, and a fourth terminal thereof is connected to a first power supply voltage terminal VSS. The pull-down circuit 33 is configured to pull down the output terminal OUTPUT and the pull-up node PU to the first power supply voltage of the first power supply voltage terminal VSS when the pull-down signal of the pull-down node PD is at a valid pull-down level.

A first terminal of the first pull-down control circuit 35 is connected to a second clock signal terminal CLKB, a second terminal thereof is connected to a first pull-down control node PD_CN1, a third terminal thereof is connected to the pull-down node PD, a fourth terminal thereof is connected to the pull-up node PU, and a fifth terminal thereof is connected to the first power supply voltage terminal VSS. The first pull-down control circuit 35 is configured to pull down the pull-down node PD to the first power supply voltage of the first power supply voltage terminal VSS when the pull-up signal of the pull-up node PU is at a valid pull-up level, and to output the second clock signal of the second clock signal terminal CLKB to the pull-down node PD when the first pull-down control node PD_CN1 is at a first voltage.

A first terminal of the second pull-down control circuit 36 is connected to the second clock signal terminal CLKB, a second terminal thereof is connected to the first power supply voltage terminal VSS, a third terminal thereof is connected to the pull-up node PU, a fourth terminal thereof is connected to the first pull-down control node PD_CN1, and a fifth terminal thereof is connected to a second power supply voltage terminal VGH. The second pull-down control circuit 36 is configured to: pull down the first pull-down control node PD_CN1 to the first power supply voltage of the first power supply voltage terminal VSS when the pull-up signal of the pull-up node PU is at a valid pull-up level, and to compensate for the voltage of the first pull-down control node PD_CN1 through the second power supply voltage when the pull-up signal of the pull-up node PU is at an invalid pull-up level and the second clock signal of the second clock signal terminal CLKB is at a first level, so that the voltage of the first pull-down control node PD_CN1 is capable of driving the first pull-down control circuit 35 normally to output the second clock signal to the pull-down node PD.

In this embodiment, phase of the first clock signal of the first clock signal terminal CLK is inverted compared to that of the second clock signal of the second clock signal terminal CLKB.

In this embodiment, the first power supply voltage terminal VSS is a low power supply voltage terminal.

According to an embodiment of the present disclosure, the second power supply voltage terminal VGH is a high power supply voltage terminal. Further, for example, the second power supply voltage of the second power supply voltage terminal VGH is higher than the voltage of the first level of the second clock signal.

According to the embodiment of the present disclosure, for example, the second pull-down control circuit 36 comprises: a first pull-down control transistor M8, a second pull-down control transistor M7 and a pull-down compensation sub-circuit.

A gate of the first pull-down control transistor M8 is connected to the pull-up node PU, a first electrode thereof is connected to the first pull-down control node PD_CN1, a second electrode thereof is connected to the first power supply voltage terminal VSS. A gate and a first electrode of the second pull-down control transistor M7 are connected to the second clock signal terminal CLKB, and a second electrode thereof is connected to the second pull-down control node PD_CN2.

According to an embodiment of the present disclosure, for example, the pull-down compensation sub-circuit is connected to the second power supply voltage terminal VGH, the second clock signal terminal CLKB, the first pull-down control node PD_CN1 and the second pull-down control node PD_CN2. The pull-down compensation sub-circuit is configured to: compensate for voltage drift of the second pull-down control node PD_CN2 caused by threshold voltage drift of the second pull-down control transistor M7 through the second power supply voltage when the pull-up signal of the pull-up node PU is at an invalid pull-up level and the second clock signal of the second clock signal terminal CLKB is at a first level, and further compensate for the first pull-down control node PD_CN1 to make it stable at the first voltage, wherein the first voltage enables the first pull-down control node PD_CN1 to normally drive the first pull-down control circuit 35 to output the second cock signal to the pull-down node PD, so as to further control the pull-down circuit 33 for discharging the pull-up node PU and the output terminal OUTPUT reliably.

It shall be noted that the embodiments described herein concerning the pull-down compensation sub-circuit are just a part of embodiments of the present disclosure, but not all the embodiments. Based on the embodiments in the present disclosure, all other embodiments of setting a corresponding circuit module with respect to different shift register units to suppress the threshold voltage drift of the TFT so as to enhance the stability of the shift register unit belong to the scope sought for protection in the present disclosure.

Optionally, in another embodiment, the input circuit 31 of the shift register unit 300 further comprises a third terminal connected to the second clock signal terminal CLKB. The input circuit 31 is further configured to output the input signal of the input terminal INPUT to the pull-up node PU under control of the second clock signal terminal CLKB, to enhance an inputting capability of the input terminal INPUT for the pull-up node PU, so that the pull-up node PU is enhanced when being at a valid pull-up level and is reduced noise when being at an invalid pull-up level.

Optionally, in another embodiment, the shift register unit 300 further comprises a reset circuit 34.

For example, a first terminal of the reset circuit 34 is connected to a reset signal terminal RESET, a second terminal thereof is connected to the pull-up node PU, a third terminal thereof is connected to the first power supply voltage terminal VSS, and a fourth terminal thereof is connected to the output terminal OUTPUT. The reset circuit 34 is configured to pull down the pull-up signal of the pull-up node PU and the output signal of the output terminal OUTPUT to the first power supply voltage of the first power supply voltage terminal VSS when the reset signal of the reset signal terminal RESET is at a valid reset level.

Optionally, in another embodiment, the shift register unit 300 further comprises a noise reduction circuit 37.

For example, a first terminal of the noise reduction circuit 37 is connected to the second clock signal terminal CLKB, a second terminal thereof is connected to the first power supply voltage terminal VSS, a third terminal thereof is connected to the output terminal OUTPUT. The noise reduction circuit 37 is configured to pull down the output terminal OUTPUT to the first power supply voltage of the first power supply voltage terminal VSS when the second clock signal of the second clock signal terminal CLKB is at a first level, so as to enhance a noise reduction capability for the output terminal OUTPUT.

FIG. 4 shows an exemplary circuit structure diagram of a shift register unit according to an embodiment of the present disclosure. Descriptions are given below by taking the transistors in FIG. 4 being N type transistors as an example. As well known by those skilled in the art, the N type transistors are turned on when high levels are input to gates of the N type transistors.

As shown in FIG. 4, in an embodiment, for example, the input circuit 31 comprises a first input transistor M1, whose gate and first electrodes are connected to the input terminal INPUT, and second electrode is connected to the pull-up node PU. When the input signal of the input terminal INPUT is at a high level, the first input transistor M1 is turned on to output the input signal of the input terminal INPUT to the pull-up node PU.

Optionally, in another embodiment, for example, the input circuit 31 further comprises a second input transistor M11, whose gate is connected to the second clock signal terminal CLKB, first electrode is connected to the input terminal INPUT, and second electrode is connected to the pull-up node PU. When the second clock signal of the second clock signal terminal CLKB is at a high level, the second input transistor M11 is turned on to output the input signal of the input terminal INPUT to the pull-up node PU.

In an embodiment, for example, the output circuit 32 comprises an output transistor M2 and a first capacitor C1. A gate of the output transistor M2 and a first terminal of the first capacitor C1 are connected to the pull-up node PU, a first electrode of the output transistor M2 is connected to the first clock signal terminal CLK, and a second electrode of the output transistor M2 and a second terminal of the first capacitor C1 are connected to the output terminal OUTPUT. When the pull-up signal of the pull-up node PU is at a high level, the output transistor M2 is turned on to output the first clock signal of the first clock signal terminal CLK to the output terminal OUTPUT.

In an embodiment, for example, the pull-down circuit 33 comprises a first pull-down transistor M9 and a second pull-down transistor M10. Both a gate of the first pull-down transistor M9 and a gate of the second pull-down transistor M10 are connected to the pull-down node PD, both a second electrode of the first pull-down transistor M9 and a second electrode of the second pull-down transistor M10 are connected to the first power supply voltage terminal VSS, a first electrode of the first pull-down transistor M9 is connected to the pull-up node PU, and a first electrode of the second pull-down transistor M10 is connected to the output terminal OUTPUT. When the pull-down signal of the pull-down node PD is at a high level, both the first pull-down transistor M9 and the second pull-down transistor M10 are turned on to pull down the pull-up node PU and the output terminal OUTPUT to the first power supply voltage of the first power supply voltage terminal VSS respectively.

In an embodiment, for example, the first pull-down control circuit 35 comprises a third pull-down control transistor M5 and a fourth pull-down control transistor M6. A gate of the third pull-down control transistor M5 is connected to the first pull-down control node PD_CN1, a first electrode thereof is connected to the second clock signal terminal CLKB, and a second electrode thereof is connected to the pull-down node PD; a gate of the fourth pull-down control transistor M6 is connected to the pull-up node PU, a first electrode thereof is connected to the pull-down node PD, and a second electrode thereof is connected to the first power supply voltage terminal VSS. When the pull-up signal of the pull-up node PU is at a high level, the fourth pull-down control transistor M6 is turned on to pull down the pull-down node PD to the first power supply voltage of the first power supply voltage terminal VSS. When the first pull-down control node PD_CN1 is at a first voltage, the third pull-down control transistor M5 is turned on to output the second clock signal of the second clock signal terminal CLKB to the pull-down node PD, wherein the first voltage of the first pull-down control node PD_CN1 refers to a voltage enough to drive the third pull-down control transistor M5 to be turned on.

In an embodiment, for example, the second pull-down control circuit 36 comprises a first pull-down control transistor M8, a second pull-down control transistor M7 and a pull-down compensation sub-circuit. Further, for example, the pull-down compensation sub-circuit comprises a first pull-down compensation transistor M13 and a second pull-down compensation transistor M14. A gate of the first pull-down compensation transistor M13 is connected to the second clock signal terminal CLKB, a first electrode of the first pull-down compensation transistor M13 and a second electrode of the second pull-down compensation transistor M14 are connected to the second pull-down control node PD_CN2, a second electrode of the first pull-down compensation transistor M13 and a gate of the second pull-down compensation transistor M14 are connected to the first pull-down control node PD_CN1, and a first electrode of the second pull-down compensation transistor M14 is connected to the second power supply voltage terminal VGH. In addition, in the embodiment, a relationship of channel width-to-length ratios among the second pull-down control transistor M7, the first pull-down compensation transistor M13 and the first pull-down control transistor M8 is configured properly, so that turn-on resistance of the first pull-down control transistor M8 is far smaller than total turn-on resistance of the second pull-down control transistor M7 and the first pull-down compensation transistor M13.

In the embodiment, for example, the second power supply voltage of the second power supply voltage terminal VGH is higher than a high level voltage of the second clock signal. Further, for example, a selection of the second power supply voltage of the second power supply voltage terminal VGH can be configured according to channel width-to-length ratios of the third pull-down control transistor M5 and the fourth pull-down control transistor M6, to ensure that a voltage of the first pull-down control node PD_CN1 during the process of pulling down is enough to drive the third pull-down control transistor M5 to be turned on successfully.

Optionally, in an embodiment, for example, the reset circuit 34 comprises a first reset transistor M3 and a second reset transistor M4. Both a gate of the first reset transistor M3 and a gate of the second reset transistor M4 are connected to the reset signal terminal RESET, both a second electrode of the first reset transistor M3 and a second electrode of the second reset transistor M4 are connected to the first power supply voltage terminal VSS, a first electrode of the first reset transistor M3 is connected to the pull-up node PU, and a first electrode of the second reset transistor M4 is connected to the output terminal OUTPUT. When the reset signal of the reset signal terminal RESET is at a high level, both the first reset transistor M3 and the second reset transistor M4 are turned on to pull down the pull-up signal of the pull-up node PU and the output signal of the output terminal OUTPUT to the first power supply voltage of the first power supply voltage terminal VSS respectively.

Optionally, in an embodiment, for example, the noise reduction circuit 37 comprises a noise reduction transistor M12, whose gate is connected to the second clock signal terminal CLKB, first electrode is connected to the output terminal OUTPUT, and second electrode is connected to the first power supply voltage terminal VSS. When the second clock signal of the second clock signal terminal CLKB is at a high level, the noise reduction transistor M12 is turned on to pull down the output terminal OUTPUT to the first power supply voltage of the first power supply voltage terminal VSS, so as to reduce the noise of the output terminal OUTPUT.

FIG. 5 shows an operation timing diagram of an exemplary circuit of the shift register unit shown in FIG. 4. The driving method of the shift register unit shown in FIG. 4 is described below by combining FIGS. 4 and 5.

In a first phase P1, the input terminal INPUT is at a high level, and the first input transistor M1 is turned on to output the high level of the input terminal INPUT to the pull-up node PU. At this time, the pull-up node PU is at the high level, so that the output transistor M2 is turned on. Since the first clock signal of the first clock signal terminal CLK is at a low level, the output terminal OUTPUT outputs the low level. Since the pull-up node PU is at the high level, the fourth pull-down control transistor M6 and the first pull-down control transistor M8 are turned on to pull down the pull-down node PD and the first pull-down control node PD_CN1 respectively, and correspondingly the first pull-down transistor M9, the second pull-down transistor M10, the third pull-down control transistor M5 and the second pull-down compensation transistor M14 are turned off. In addition, in this phase, the second clock signal terminal CLKB is at a high level, and both the second pull-down control transistor M7 and the first pull-down compensation transistor M13 are turned on. Since turn-on resistance of the first pull-down control transistor M8 is far smaller than total turn-on resistance of the second pull-down control transistor M7 and the first pull-down compensation transistor M13, the potential of the first pull-down control node PD_CN1 is at a low level in this phase.

Alternatively, in this phase, the reset signal of the reset signal terminal RESET is at a low level, and both the first reset transistor M3 and the second reset transistor M4 are turned off. Optionally, in this phase, under driving of a high level of the second clock signal terminal CLKB, the noise reduction transistor M12 is turned on to reduce the noise of the output terminal OUTPUT. Optionally, in this phase, the second input transistor M11 is also turned on, which enhances the high level outputted by the input terminal INPUT to the pull-up node PU.

In a second phase P2, the input terminal INPUT is at a low level, the first input transistor M1 is turned off. Since the pull-up node PU has been already at the high level before, the output transistor M2 maintains turned on. Further, the first clock signal of the first clock signal terminal CLK is at a high level, thus the output terminal OUTPUT outputs the high level. Due to voltage coupling effect of the first capacitor C1, as the potential of the output terminal OUTPUT rises, the potential of the pull-up node PU further rises. In addition, in this phase, since the pull-up node PU is still at a high level, the fourth pull-down control transistor M6 and the first pull-down control transistor M8 remain turned on, and the pull-down node PD and the first pull-down control node PD_CN1 are still at a low level, and correspondingly all of the first pull-down transistor M9, the second pull-down transistor M10, the third pull-down control transistor M5 and the second pull-down compensation transistor M14 maintain turned off. Optionally, in this phase, the reset signal of the reset signal terminal RESET is at a low level, and the first reset transistor M3 and the second reset transistor M4 maintain turned off. Optionally, in this phase, since the second clock signal terminal CLKB is at a low level, the noise reduction transistor M12 is turned off. Optionally, in this phase, the second input transistor M11 is turned off.

In a third phase P3, the input terminal INPUT is at a low level, and the first input transistor M1 maintains turned off. On one hand, optionally, the reset signal of the reset signal terminal RESET is at a high level, and the first reset transistor M3 and the second reset transistor M4 are turned on to pull down the pull-up signal of the pull-up node PU and the output signal of the output terminal OUTPUT to the first power supply voltage of the first power supply voltage terminal VSS respectively. On the other hand, since the second clock signal terminal CLKB is at a high level, the second pull-down control transistor M7 and the first pull-down compensation transistor M13 are turned on, so that both the first pull-down control node PD_CN1 and the second pull-down control node PD_CN2 are at a high level. At this time, the high level of the first pull-down control node PD_CN1 further drives the second pull-down compensation transistor M14 to be turned on The high level of the second power supply voltage terminal VGH is compensated to the second pull-down control node PD_CN2 through the second pull-down compensation transistor M14, so that the voltage of the second pull-down control node PD_CN2 is maintained stable without being influenced by positive drift of the threshold voltage of the second pull-down control transistor M7, and thus the potential of the first pull-down control node PD_CN1 is maintained at the high level, through the first pull-down compensation transistor M13, which is enough to drive the third pull-down control transistor M5 to be turned on. Since the third pull-down control transistor M5 is turned on, the high level of the second clock signal terminal CLKB is output to the pull-down node PD, so that the voltage of the pull-down node PD jumps from the low level into the high level, and correspondingly both the first pull-down transistor M9 and the second pull-down transistor M10 are turned on to pull down the pull-up node PU and the output terminal OUTPUT to the low level respectively. In addition, in this phase, since the pull-up node PU is at the low level, all of the fourth pull-down control transistor M6, the first pull-down control transistor M8 and the output transistor M2 are turned off. Optionally, in this phase, under driving of the high level of the second clock signal terminal CLKB, the noise reduction transistor M12 is turned on, which reduces the noise of the output terminal OUTPUT. Optionally, in this phase, the second input transistor M11 is also turned on, so that the low level of the input terminal INPUT further reduces the noise of the pull-up node PU.

In a phase P4, the input terminal INPUT is at a low level, the first input transistor M1 maintains turned off, the pull-up node PU maintains at a low level, all of the fourth pull-down control transistor M6, the first pull-down control transistor M8 and the output transistor M2 maintain turned off. The second clock signal terminal CLKB is at a low level, and both the second pull-down control transistor M7 and the first pull-down compensation transistor M13 are turned off. The pull-down node PD is discharged to the low level, the first pull-down control node PD_CN1 is discharged to a second voltage which is higher than a zero voltage and lower than its first voltage, and both the third pull-down control transistor M5 and the second pull-down compensation transistor M14 are turned off. Optionally, both the second input transistor M11 and the noise reduction transistor M12 are turned off. Optionally, in this phase, both the first reset transistor M3 and the second reset transistor M4 are turned off.

In a fifth phase P5, the input terminal INPUT is at a low level, thus the first input transistor M1 maintains turned off. The pull-up node PU maintains at a low level, thus the fourth pull-down control transistor M6, the first pull-down control transistor M8 and the output transistor M2 all maintain turned off. Since the second clock signal terminal CLKB is at a high level, both the second pull-down control transistor M7 and the first pull-down compensation transistor M13 are turned on, so that both the first pull-down control node PD_CN1 and the second pull-down control node PD_CN2 are at a high level. At this time, the high level of the first pull-down control node PD_CN1 further drives the second pull-down compensation transistor M14 to be turned on. The high level of the second power supply voltage terminal VGH is compensated to the second pull-down control node PD_CN2 through the second pull-down compensation transistor M14, so that the voltage of the second pull-down control node PD_CN2 maintains stable without being influenced by positive drift of the threshold voltage of the second pull-down control transistor M7, and thus the potential of the first pull-down control node PD_CN1 is maintained at the high level, through the first pull-down compensation transistor M13, which is enough to drive the third pull-down control transistor M5 to be turned on. Since the third pull-down control transistor M5 is turned on, the high level of the second clock signal terminal CLKB is output to the pull-down node PD, so that the voltage of the pull-down node PD jumps from the low level to the high level, and correspondingly both the first pull-down transistor M9 and the second pull-own transistor M10 are turned on to pull down the pull-up node PU and the output terminal OUTPUT to the low level respectively. Optionally, in this phase, the first reset transistor M3 and the second reset transistor M4 are turned off. Optionally, in this phase, the noise reduction transistor M12 is turned on, which reduces the noise of the output terminal OUTPUT. Optionally, in this phase, the second input transistor M11 is also turned on, so that the low level of the input terminal INPUT further reduces the noise of the pull-up node PU.

After that, before a next frame comes, the pull-up node PU is always at a low level, and under control of the second clock signal terminal CLKB, the voltage of the first pull-down control node PD_CN1 jumps at the first voltage and the second voltage alternately, the pull-down node PD jumps at the high level and the low level alternately, i.e., states of the fourth phase and the fifth phase are being repeated until the next frame comes. When the next frame comes, the shift register unit again performs the first phase described above after receiving a high level signal from the input terminal INPUT.

In the shift register unit as shown in FIG. 1, when the positive drift occurs to the threshold voltage of the seventh transistor M7, it would cause that the voltage of the pull-down control node PD_CN during the third phase P3 is reduced, which is likely to further cause that the fifth transistor M5 cannot be turned on in the third phase P3, such that the shift register unit cannot operate normally, so as to affect stability of the shift register unit.

The shift register unit as shown in FIG. 4 according to the embodiment of the present disclosure is additionally provided with the first pull-down compensation transistor M13 and the second pull-down compensation transistor M14, and is accessed to the second power supply voltage terminal VGH.

On one hand, in the above third phase P3 and the above fifth phase P5, since the second clock signal of the second clock signal terminal CLKB is at a high level, the second pull-down control transistor M7 and the first pull-down compensation transistor M13 are turned on. At a moment when the second pull-down control transistor M7 is turned on, the threshold voltage of the second pull-down control transistor M7 has not drifted yet or is only slightly drifted, and at this time, voltages of the first pull-down control node PD_CN1 and the second pull-down control node PD_CN2 are still not reduced by the influence of the threshold voltage drift of the second pull-down control transistor M7 or are reduced a little, thus the high voltage of the first pull-down control node PD_CN1 is enough to drive the second pull-down compensation transistor M14 to be turned on, then the high level of the second power supply voltage terminal VGH is compensated to the second pull-down control node PD_CN2 through the second pull-down compensation transistor M14, so that the voltage of the second pull-down control node PD_CN2 is maintained stable in subsequent processes, wherein the second power supply voltage of the second power supply voltage terminal VGH is higher than the high level voltage of the second clock signal of the second clock signal terminal CLKB. Therefore, even if a large positive drift occurs to the threshold voltage of the second pull-down control transistor M7 after it has operated for a period of time, which causes that output voltage of the second electrode of the second pull-down control transistor M7 is reduced, the voltage of the second pull-down control node PD_CN2 can also be maintained stable continuously under compensation of the second power supply voltage terminal VGH. Further, the first pull-down compensation transistor M13 enables the potential of the first pull-down control node PD_CN1 to be maintained at the first voltage which is enough to drive the third pull-down control transistor M5 to be turned on, so as to suppress bad influence produced by the threshold voltage drift of the second pull-down control transistor M7 on the shift register unit.

On the other hand, the high voltage (for example, higher than the high level voltage of the second clock signal terminal) of the second power supply voltage terminal VGH is connected to the first electrode of the first pull-down compensation transistor M13 through the second pull-down compensation transistor M14, so that a voltage difference between a first electrode and a second electrode of the first pull-down compensation transistor M13 is decreased, i.e., a voltage difference between a source and a drain of the first pull-down compensation transistor M13 is decreased. In this case, although positive drift is also likely to occur to the first pull-down compensation transistor M13, the above circuit design makes the voltage difference between the source and the drain of the first pull-down compensation transistor M13 decreased, which suppresses the threshold voltage drift of the first pull-down compensation transistor M13, so as to ensure that, when the second clock signal terminal CLKB outputs a high level, the first pull-down control node PD_CN1 is capable of being stabilized at the first voltage having a high level which is enough to drive the third pull-down control transistor M5 to be turned on, so that the first pull-down control circuit can drive the pull-down circuit normally to realize discharging the pull-up node PU and the output terminal OUTPUT reliably, thus avoiding abnormality of the output signal of the shift register unit, and further ensuring the stability of the shift register unit, prolonging service life of the TFT-LCD on which the shift register unit is applied, and enhancing picture quality of the TFT-LCD display device.

There is provided in the present disclosure a driving method of the shift register unit described above. FIG. 6 shows an exemplary driving method of a shift register unit according to an embodiment of the present disclosure. By referring to FIG. 6, the method is described below by combining with FIGS. 3 and 5. In an embodiment, for example, as shown in FIG. 3, the shift register unit 300 comprises an input circuit 31, an output circuit 32, a pull-down circuit 33, a first pull-down control circuit 35 and a second pull-down control circuit 36. The driving method of the shift register unit comprises:

In step 601, when the input signal of the input terminal INPUT is at a valid input level, receiving the input signal and outputting it to the pull-up node PU by the input circuit 31;

In step 602, when the pull-up node PU is at a valid pull-up level, pulling down the pull-down node PD to the first power supply voltage of the first power supply voltage terminal VSS by the first pull-down control circuit 35, pulling down the first pull-down control node PD_CN1 to the first power supply voltage of the first power supply voltage terminal VSS by the second pull-down control circuit 36, and outputting the first clock signal of the first clock signal terminal CLK to the output terminal OUTPUT by the output circuit 32;

In step 603, when the pull-up node PU is at an invalid pull-up level and the second clock signal terminal CLKB is at the first level, the first pull-down control node PD_CN1 is compensated through the second power supply voltage of the second power supply voltage terminal VGH, so that the first pull-down control node PD_CN1 is maintained at the first voltage, so as to drive the first pull-down control circuit 35 for outputting the second clock signal of the second clock signal terminal CLKB to the pull-down node PD; and

In step 604, when the pull-down node PD is at a valid pull-down level, pulling down the pull-up node PU and the output terminal OUTPUT to the first power supply voltage of the first power supply voltage terminal VSS by the pull-down circuit 33.

Herein, the first power supply voltage terminal VSS is a low power supply voltage terminal, and phase of the first clock signal of the first clock signal terminal CLK is inverted compared to that of the second clock signal of the second clock signal terminal CLKB. The second power supply voltage terminal VGH is a high power supply voltage terminal. Further, for example, the second power supply voltage of the second power supply voltage terminal VGH is higher than the high level voltage of the second clock signal.

Optionally, the shift register unit 300 further comprises a reset circuit 34. In step 603, the driving method further comprises: pulling down, by the reset unit, the pull-up node and the output terminal to the first power supply voltage of the first power supply voltage terminal, when the reset signal of the reset signal terminal is at a valid level.

Optionally, the shift register unit 300 further comprises a noise reduction circuit 37. In steps 601 and 603, the driving method further comprises: pulling down, by the noise reduction unit, the output terminal of the shift register unit to the first power supply voltage of the first power supply voltage terminal, when the second clock signal of the second clock signal terminal is at a valid level.

In the shift register unit and the driving method thereof according to the embodiment of the present disclosure, by adding a related pull-down compensation module to the pull-down control circuit, the influence of the positive drift of the threshold voltage of the second pull-down control transistor M7 driven by a long-time high voltage of the clock signal on the first pull-down control node is compensated, so that the first pull-down control node is capable of driving the pull-down circuit normally, which avoids abnormality of the output signal of the shift register unit, and thus ensure stability of the shift register unit, prolong the service life of the TFT-LCD on which the shift register unit is applied, and enhance the picture quality of the TFT-LCD display device.

FIG. 7 shows a schematic diagram of a gate driving device formed by a plurality of shift register units connected in series according to an embodiment of the present disclosure.

As shown in FIG. 7, in the gate driving device, a plurality of shift register units as shown in FIG. 4 are connected in series, wherein except a last shift register unit Rm, an output terminal OUTPUT of each of remaining shift register units Ri (1≤i<m) is connected to an input terminal INPUT of a next adjacent shift register unit Ri+1. Except a first shift register unit R1, an output terminal OUTPUT of each of remaining shift register units Ri (1<i≤m) is connected to a reset signal terminal RESET of a previous adjacent shift register unit Ri-1. The input terminal of the first shift register unit R1 is input a frame start signal STV.

As shown in FIG. 5, in the gate driving device, clock signals input to clock signal terminal of two adjacent stages of shift register units are opposite. For example, the first shift register unit R1 is input a clock signal CLK, then the second shift register unit R2 is input a clock signal CLKB, wherein the CLK signal and the CLKB signal have phases inverted to each other.

When scanning is performed, specific operation processes of respective shift register units of the gate driving device according to the embodiment of the present disclosure are similar to the operation processes described by referring to FIGS. 4 and 5, and thus no further description is given herein.

The gate driving device according to an embodiment of the present disclosure can adopt the GOA technique to be used as the gate driving circuit of the display device, to provide the function of progressive scanning and deliver the scanning signal to the display area.

The gate driving device according to an embodiment of the present disclosure can avoid abnormality of the output signal of the shift register unit, which is caused by the positive drift of the threshold voltage produced by transistors driven by the long-term high voltage of the clock signal, thereby ensuring the stability of the shift register unit, so that the service life of the TFT-LCD on which the shift register unit is applied is prolonged, and the picture quality of the TFT-LCD display device is improved.

There is further provided in the present disclosure a display device comprising the gate driving device.

The display device herein can be any product or means having the function of displaying, such as an electronic paper, a mobile phone, a panel computer, a television set, a display, a notebook computer, a digital photo frame, a navigator, etc.

The display device according to an embodiment of the present disclosure can avoid abnormality of the output signal of the shift register unit, which is caused by the positive drift of the threshold voltage produced by transistors driven by the long-time high voltage of the clock signal, thereby ensuring the stability of the shift register unit, so that the service life of the TFT-LCD on which the shift register unit is applied is prolonged, and the picture quality of the TFT-LCD display device is improved.

The above descriptions are specific embodiments of the present disclosure, but the protection scope of the present disclosure is not limited thereto. Any alternation or replacement that can be conceived easily by those skilled in the art who are familiar with the technical field within the technical scope disclosed in the present disclosure shall be covered within the protection scope of the present disclosure. Therefore, the protection scope of the present disclosure shall be subject to the protection scope of the claims. 

What is claimed is:
 1. A shift register unit, comprising: an input circuit, whose first terminal receives an input signal of the shift register unit and second terminal is connected to a pull-up node, the input circuit being configured to output the input signal to the pull-up node; an output circuit, whose first terminal is connected to a first clock signal terminal, second terminal is connected to the pull-up node, and third terminal is connected to an output terminal of the shift register unit, the output circuit being configured to output a first clock signal of the first clock signal terminal to the output terminal under control of the pull-up node; a pull-down circuit, whose first terminal is connected to a pull-down node, second terminal is connected to the pull-up node, third terminal is connected to the output terminal, and fourth terminal is connected to a first power supply voltage terminal, the pull-down circuit being configured to pull down the pull-up node and the output terminal to a first power supply voltage of the first power supply voltage terminal under control of the pull-down node; a first pull-down control circuit, whose first terminal is connected to a second clock signal terminal, second terminal is connected to a first pull-down control node, third terminal is connected to the pull-down node, fourth terminal is connected to the pull-up node, and fifth terminal is connected to the first power supply voltage terminal, the first pull-down control circuit being configured to pull down the pull-down node to the first power supply voltage of the first power supply voltage terminal under control of the pull-up node, and to output a second clock signal of the second clock signal terminal to the pull-down node under control of the first pull-down control node; and a second pull-down control circuit, whose first terminal is connected to the second clock signal terminal, second terminal is connected to the first power supply voltage terminal, third terminal is connected to the pull-up node, fourth terminal is connected to the first pull-down control node, and fifth terminal is connected to a second power supply voltage terminal, and the second pull-down control circuit being configured to pull down the first pull-down control node to the first power supply voltage of the first power supply voltage terminal when the pull-up node is at a valid pull-up level, and to compensate for the first pull-down control node through a second power supply voltage when the pull-up node is at an invalid pull-up level and the second clock signal is at a first level, so that the first pull-down control node drives the first pull-down control circuit to output the second clock signal to the pull-down node.
 2. The shift register unit according to claim 1, wherein the second pull-down control circuit comprises: a first pull-down control transistor, whose gate is connected to the pull-up node, first electrode is connected to the first pull-down control node, and second electrode is connected to the first power supply voltage terminal; a second pull-down control transistor, whose gate and first electrodes are connected to the second clock signal terminal, and second electrode is connected to a second pull-down control node; and a pull-down compensation sub-circuit, connected to the second power supply voltage terminal, the second clock signal terminal, the first pull-down control node and the second pull-down control node, wherein the pull-down compensation sub-circuit is configured to compensate, by the second power supply voltage, a voltage drift of the second pull-down control node caused by a threshold voltage drift of the second pull-down control transistor, and to further compensate the first pull-down control node to make it stabilized at a first voltage, when the pull-up node is at an invalid pull-up level and the second clock signal is at a first level, wherein the first voltage drives the first pull-down control circuit to output the second clock signal to the pull-down node.
 3. The shift register unit according to claim 2, wherein the pull-down compensation sub-circuit comprises: a first pull-down compensation transistor, whose gate is connected to the second clock signal terminal, first electrode is connected to the second pull-down control node, and second electrode is connected to the first pull-down control node; and a second pull-down compensation transistor, whose gate is connected to the first pull-down control node, first electrode is connected to the second power supply voltage terminal, and second electrode is connected to the second pull-down control node.
 4. The shift register unit according to claim 1, wherein the input circuit further comprises a third terminal connected to the second clock signal terminal.
 5. The shift register unit according to claim 1, further comprising: a reset circuit, whose first terminal is connected to a reset signal terminal, second terminal is connected to the pull-up node, third terminal is connected to the first power supply voltage terminal, and fourth terminal is connected to the output terminal, the reset circuit being configured to pull down the pull-up node and the output terminal to the first power supply voltage of the first power supply voltage terminal under control of the reset signal terminal.
 6. The shift register unit according to claim 1, further comprising: a noise reduction circuit, whose first terminal is connected to the second clock signal terminal, second terminal is connected to the first power supply voltage terminal, third terminal is connected to the output terminal, the noise reduction circuit being configured to pull down the output terminal to the first power supply voltage of the first power supply voltage terminal under control of the second clock signal terminal.
 7. The shift register unit according to claim 1, wherein the input circuit comprises: a first input transistor, whose gate and first electrodes are connected to the input terminal, and second electrode is connected to the pull-up node.
 8. The shift register unit according to claim 6, wherein the input circuit further comprises: a second input transistor, whose gate is connected to the second clock signal terminal, first electrode is connected to the input terminal, and second electrode is connected to the pull-up node.
 9. The shift register unit according to claim 1, wherein the output circuit comprises: an output transistor, whose gate is connected to the pull-up node, first electrode is connected to the first clock signal terminal, second electrode is connected to the output terminal; and a first capacitor, whose first terminal is connected to the pull-up node, and second terminal is connected to the output terminal.
 10. The shift register unit according to claim 1, wherein the pull-down circuit comprises: a first pull-down transistor, whose gate is connected to the pull-down node, first electrode is connected to the pull-up node, and second electrode is connected to the first power supply voltage terminal; and a second pull-down transistor, whose gate is connected to the pull-down node, first electrode is connected to the output terminal, and second electrode is connected to the first power supply voltage terminal.
 11. The shift register unit according to claim 1, wherein the first pull-down control circuit comprises: a third pull-down control transistor, whose gate is connected to the first pull-down control node, first electrode is connected to the second clock signal terminal, and second electrode is connected to the pull-down node; and a fourth pull-down control transistor, whose gate is connected to the pull-up node, first electrode is connected to the pull-down node, and second electrode is connected to the first power supply voltage terminal.
 12. The shift register unit according to claim 5, wherein the reset circuit comprises: a first reset transistor, whose gate is connected to a reset signal terminal, first electrode is connected to the pull-up node, and second electrode is connected to the first power supply voltage terminal; and a second reset transistor, whose gate is connected to the reset signal terminal, first electrode is connected to the output terminal, and second electrode is connected to the first power supply voltage terminal.
 13. The shift register unit according to claim 6, wherein the noise reduction circuit comprises: a noise reduction transistor, whose gate is connected to the second clock signal terminal, first electrode is connected to the output terminal, and second electrode is connected to the first power supply voltage terminal.
 14. The shift register unit according to claim 11, wherein the second power supply voltage of the second power supply voltage terminal is selected according to channel width-to-length ratios of the third pull-down control transistor and the fourth pull-down control transistor.
 15. A driving method for the shift register unit according to claim 1, comprising: receiving an input signal of the shift register unit and outputting the input signal to a pull-up node, by an input circuit, when the input signal is at a valid input level; pulling down, by a first pull-down control circuit, a pull-down node to a first power supply voltage of a first power supply voltage terminal, pulling down, by a second pull-down control circuit, a first pull-down control node to the first power supply voltage of the first power supply voltage terminal, and outputting, by an output circuit, a first clock signal of a first clock signal terminal to an output terminal, when the pull-up node is at a valid pull-up level; compensating the first pull-down control node by a second power supply voltage when the pull-up node is at an invalid pull-up level and a second clock signal is at a first level, such that the first pull-down control node is maintained at a first voltage, so as to drive the first pull-down control circuit for outputting the second clock signal of a second clock signal terminal to the pull-down node; pulling down, by a pull-down circuit, the pull-up node and the output terminal to the first power supply voltage of the first power supply voltage terminal, when the pull-down node is at a valid pull-down level.
 16. The driving method according to claim 15, wherein the second power supply voltage of a second power supply voltage terminal is higher than a voltage of the first level of the second clock signal.
 17. The driving method according to claim 15, wherein the second pull-down control circuit comprises: a first pull-down control transistor, whose gate is connected to the pull-up node, first electrode is connected to the first pull-down control node, and second electrode is connected to the first power supply voltage terminal; a second pull-down control transistor, whose gate and first electrodes are connected to the second clock signal terminal, and second electrode is connected to a second pull-down control node; and a pull-down compensation sub-circuit, connected to the second power supply voltage terminal, the second clock signal terminal, the first pull-down control node and the second pull-down control node, wherein compensating the first pull-down control node by the second power supply voltage comprises: compensating a voltage drift of the second pull-down control transistor on the second pull-down control node by the second power supply voltage, and further compensating the first pull-down control node to make it stabilized at a first voltage.
 18. A Gate driving device, comprising a plurality of shift register units connected in series, each of which is the shift register unit according to claim 1, wherein except a last shift register unit, an output terminal of each of remaining shift register units is connected to an input terminal of a next adjacent shift register unit; a frame start signal is inputted to an input terminal of a first shift register unit.
 19. A display device comprising the gate driving device according to claim
 18. 